Point of sale (POS) terminals allow customers to make payments using a variety of payment instruments, such as credit cards, debit cards, smart cards and ATM cards. To ensure that the payment information transmitted from the POS terminals to a payment center is not accessed by unauthorized recipients, this information is typically encrypted and secured (e.g., using digital authentication) during transmission. However, confidential payment information entered by the user into the POS terminal could still be intercepted by tampering with the integrated circuits of the POS terminal. Thieves can use such information fraudulently to receive payment. It may also be desirable to maintain confidentiality of integrated circuit device layouts to prevent thieves from copying integrated circuit designs. Clearly the need to prevent unauthorized access to integrated circuits is present.
U.S. Pat. No. 4,811,288 describes a technique to prevent unauthorized access to a memory device through the use of a conductive mesh outside of the memory device. To access the memory device, a thief must cut through the conductive mesh. Cutting through the mesh, however, alters the conductive properties of the mesh. Altering portions of the conductive mesh can change impedances, create short circuits, and/or create open circuits. Detection of a change in an impedance, short circuits and/or open circuits is associated with tampering and in turn causes the memory to become erased. Thereby, unauthorized access to memory is prevented. However, use of such a mesh wire bond cage is expensive. Purchasers of integrated circuits are often very cost sensitive.